1. Field of the Invention
The invention relates to a turbomachine for low-temperature applications, having a housing, a rotor shaft mounted in the housing, an impeller disposed on a shaft end of the rotor shaft, to which a cold gas is applied, and an electrical machine integrated into the housing. The electrical machine has a rotor disposed on the rotor shaft and stator windings disposed on the housing. A cold zone forms within the housing, in the impeller-side end, during operation of the turbomachine, and a warm zone forms at the end facing away from the impeller.
2. The Prior Art
Turbomachines having the above-mentioned characteristics are described in German Patent No. DE 103 10 677 A1 and from practice, in various embodiments., and are used for compression and transport of evaporating liquid gas (LNG) or for relaxation of gases in connection with the cryogenic decomposition of air. The electrical machine works either as a drive motor of a turbocompressor, or as an energy-recovering power generator for braking an expansion turbine. Turbomachines in which the impeller and the rotor of the electrical machine are disposed on a common shaft are operated at high speeds of rotation, resulting in significant heat development, both in the electrical machine and in the shaft bearings. Because of operation of the turbomachine in the low-temperature range, great temperature gradients can occur in the housing, and the temperature progression is dependent on the method of operation of the turbomachine. Thus, in full-load operation, for example, at the maximum operational speed of rotation, the heat development in the electrical machine as well as in the bearings, particularly at the free shaft end, which heat development is not insignificant, will result in significant heating, which requires cooling, in order to protect the bearings and parts of the electrical machine against thermal overheating. In partial-load operation, i.e., at low power of the electrical machine, at a possibly reduced speed of rotation, the impeller-side end of the electrical machine as well as the impeller-side bearing are cooled extremely, specifically as a result of the heat exchange between the housing interior of the electrical machine and the bearing, and the low-temperature stage of the turbomachine. In addition, there are possible cold gas leaks from the turbomachine stage into the housing of the electrical machine, which is flanged on. Then, if the temperature goes below a permissible minimum temperature for the materials that are used in the electrical machine and in the bearings, this region must be heated.
Generally, only one compressed gas source is available for cooling and heating, for example instrument air, blocking nitrogen, or clean process gas, which is mostly available at a temperature between 10° C. and 40° C. The gas that is available as a compressed gas source, whether it is instrument air, blocking nitrogen, or clean process gas, is too warm for effective cooling and too cold for effective heating. A significant compressed gas volume stream is required both for heating the cold zone and for cooling the warm zone of the housing, which stream has a negative influence on the operating costs of the turbomachine, or actually makes additional investments for compressed gas volume production necessary.
U.S. Pat. No. 4,792,278 describes a turbomachine that is structured as a multi-stage turboexpander. The turboexpander has a rotor shaft mounted in a housing, with two end-side impellers and one rotor set onto the shaft, which works together with stator windings in the housing, as a generator. A compressed gas is first expanded in a first turbine stage, and subsequently in a second turbine stage of one of the impellers. The gas drives the generator, losing pressure, and is cooled. The gas is first guided through the first expansion stage at the end of the impeller assigned to the shaft, and subsequently through the second expansion stage at the front end of the impeller. The gas stream that is guided through the first expansion stage cools the impeller and insulates the gas stream that is guided through the second expansion stage from the housing.
U.S. Pat. No. 5,980,218 relates to a two-stage compressor having a rotor shaft mounted in a housing. The electrical machine that drives the shaft is formed by a rotor disposed on the rotor shaft and a stator winding disposed in the housing. An impeller is disposed on the ends of the rotor shaft, in each instance. Air drawn in from the surroundings is compressed in a first compression stage, and cooled in a gas cooler. Part of the gas compressed in the first compression stage and subsequently cooled is passed into the housing as a cooling gas stream, to cool the electrical machine, by way of bypass valves. The cooling gas flows through the electrical machine essentially radially, and is passed to the approach of the first compression stage via outlet openings.